“Sneak Thief of Sight” a Preventable Disease
Houston (May 22, 2002) - Glaucoma, a condition that results in damage to the optic nerve, is called the “sneak thief of sight” and is the leading cause of irreversible blindness in the United States. It has been estimated that more than 3 million people in the U.S. have glaucoma, but as many as half of those individuals may not know they have the disease.
According to Nancy E. Webb, M.D., FACS, a board-certified ophthalmologist, chief of Ophthalmology at Kelsey-Seybold Clinic and associate clinical professor of Ophthalmology at Baylor College of Medicine, the reason most people are unaware they have the disease is that usually glaucoma has no initial symptoms. “Glaucoma is usually due to elevated pressure in the eye,” the doctor explained. “The pressure can damage the optic nerve and cause a loss of vision, but the loss is very subtle. It starts with a decrease in peripheral (side) vision that is hardly noticeable.”
If glaucoma is not diagnosed and treated, it may progress from loss of side vision to loss of central vision and blindness. Because there are no early warning signs, it is important to know your risk factors and to have regular eye exams.
Certain people are at higher risk for developing glaucoma. They include:
- African-Americans over 40, who are five times more likely than Caucasians to develop glaucoma and four times more likely to develop irreversible blindness;
- Adults with severe myopia (nearsightedness);
- Individuals with diabetes or a family history of glaucoma; and
- Adults 60 years and older.
- Regardless of whether there are any risk factors, Dr. Webb urges men and women to have their eyes examined at regular intervals.
Having your vision checked for glasses is not the same thing as being screened for glaucoma. There are specific tests that a trained eye doctor uses to determine whether or not you have glaucoma or are especially likely to develop the disease. First, the eye is dilated so the doctor can examine the optic nerve. The next step is a visual field test to determine how well you see through 500 different spots. Since peripheral vision deteriorates first, this test can help pinpoint loss at the earliest, most treatable stage. The third test measures intraocular pressure within the eyes.
Three Types of Glaucoma
There are three main types of glaucoma in the adult population: chronic, acute and secondary. The most common is chronic or open-angle glaucoma, which accounts for approximately 90 percent of the cases. This condition can go undetected for many years, often until one third or more of the optic nerve has been destroyed. “With open-angle glaucoma, the tissue which filters fluid out of the eye (trabecular meshwork) looks normal, but the optic nerve doesn’t function properly. As a result, fluid doesn’t filter out of the eye at an appropriate rate, resulting in too much fluid in the eye, which leads to increased intraocular pressure,” Dr. Webb said. “There’s too much pressure within the eye, like an over-inflated tire.”
Acute, or narrow-angle, glaucoma accounts for about 10 percent of the cases. This condition occurs most often in people over age 40, who are farsighted. It also tends to run in families. With this type of glaucoma, the normal drainage passage (trabecular meshwork) between the iris (the colored portion of the eye) and cornea is blocked and pressure starts to build up inside the eye. This can lead to a sudden “attack” of glaucoma, with extremely blurred vision, seeing rainbows around lights, eye pain and sometimes nausea and vomiting.
Secondary glaucoma is generally due to chronic inflammation, or a severe injury to the eye. All three types of glaucoma can lead to blindness if left untreated.
“The best treatment option is early detection,” Dr. Webb stressed. “Once vision is lost, it can’t be restored. It’s not like a cataract (cloudiness on the lens of the eye). It is permanent nerve damage, as with a stroke or spinal cord injury. We can’t transplant the nerves yet.”
After diagnosis, glaucoma is generally treated with daily medication and drugs to control the intraocular pressure. This includes eye drops, sometimes in combination, and occasionally tablets. The next step may be laser surgery to decrease pressure in the eye. Additional surgery may be necessary in two years to create a flap in the eye to drain some of the fluid that is elevating the eye pressure. This is called “filtration surgery.”
Vision loss from glaucoma can be prevented. That’s why Dr. Webb urges men and women of all ages to have regular medical eye examinations, including glaucoma screenings. The “sneak thief of sight” can be caught before it has a chance to rob you blind.